Method for Increasing Petroleum Yield

ABSTRACT

An electrical-hydraulic method for increasing the oil yield from petroleum deposits with water- and oil-bearing rock formations in which
         a pressure-driven hydraulic water/oil volume flow ( 19 ) is continuously produced in the rock formation ( 4 ),   during a stimulation phase ( 21 ), an electrical alternating field is overlaid on the hydraulic flow field,   the electrical alternating field is generated in a controlled manner by the power converter ( 15 ),   an increase in the surface charge density is caused in the finely porous, predominantly oil-saturated regions of the rock formation ( 4 ) by the oscillating motion of the cation and anion charge carriers ( 20 ),   a mixing process with an increase in the contact surfaces and mass transfers between water and oil is produced in the water-bearing zones of the rock formation ( 4 ).   additional previously unextractable amounts of oil are mobilized and new flow paths for further transport are created.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national stage of International Application No. PCT/EP2017/070888, filed on 2017 Aug. 17. The international application claims the priority of DE 102016118282.6 filed on 2016 Sep. 27; all applications are incorporated by reference herein in their entirety.

BACKGROUND

The invention relates to a combined electrical-hydraulic oil extraction method for increasing the oil yield from conventional petroleum deposits made up of water- and oil-bearing rock formations. This involves using existing production wells as electrodes and counter electrodes in order to feed controlled functionally variable low-frequency alternating current into the producing zone at the same time as extraction is being performed by pumping. As a result of the interaction of diverse in-situ processes, additional amounts of oil are mobilized, in particular from the finely porous regions of rock. The method can be used in particular when there is increasing incursion of water during production.

Conventional petroleum deposits consist of permeable reservoir rocks, which in addition to oil also contain salty water in their porous void structure (pores, clefts, karst). Experience around the world over decades has found that only 20-40% of the total volume of oil present in such rock formations can be extracted from them by the conventional oil extraction measures, such as primary recovery by means of natural formation pressure and pumping and secondary recovery by means of additional water injection wells.

In order to increase the degree of oil extraction, conventional tertiary methods of oil extraction are used, such as for example thermal, chemical and microbiological methods and also gas injection methods, all of which require the creation of additional injection wells.

Furthermore, WO 2012/074510 A1 or U.S. Pat. No. 4,084,638 A1 for example disclose tertiary electrical methods, which use direct current or current pulses in order to lower the viscosity of heavy oil by resistive heating and thereby improve the flowability. Additional well internals in the form of independent electrodes and cable feeders down to the depths of the producing zone are required for this. In the case of a method known from U.S. Pat. No. 4,662,438 A1, alternating current is fed in by means of a pair of electrodes within an individual production well or independent bores for the electrodes have to be sunk into the producing zone.

SUMMARY

The invention relates to an electrical-hydraulic method for increasing the oil yield from petroleum deposits with water- and oil-bearing rock formations in which

-   -   a pressure-driven hydraulic water/oil volume flow (19) is         continuously produced in the rock formation (4),     -   during a stimulation phase (21), an electrical alternating field         is overlaid on the hydraulic flow field,     -   the electrical alternating field is generated in a controlled         manner by the power converter (15), continuous cycles of         functionally variable alternating current in a low-frequency         spectrum being fed in via the electrode (10) and the counter         electrode and oscillating electrical currents of the cation and         anion charge carriers (20) being caused thereby in the water-         and oil-bearing rock formation (4),     -   an increase in the surface charge density is caused in the         finely porous, predominantly oil-saturated regions of the rock         formation (4) by the oscillating motion of the cation and anion         charge carriers (20), which in turn brings about a lowering of         the interfacial viscosity and surface tension and also an         increase in the electrical repulsion between oil droplets and         the rock matrix, whereby the permeability and flow         characteristics are improved,     -   a mixing process with an increase in the contact surfaces and         mass transfers between water and oil is produced in the highly         permeable, predominantly water-bearing flow path zones of the         rock formation (4) by the oscillating motion of the cation and         anion charge carriers (20), forming highly viscous water/oil         emulsions, which cause a blocking of the highly permeable zones,     -   the blocking of the highly permeable flow path zones together         with pressure-driven volumetric flow and electrical stimulation         have the effect that additional previously unextractable amounts         of oil are mobilized and at the same time new flow paths for         further transport are created.

DETAILED DESCRIPTION

The object of the invention is to provide an electrical-hydraulic method and a device suitable for increasing the petroleum yield from petroleum deposits with water- and oil-bearing rock formations.

This object is achieved by the features of the independent claim.

The dependent claims provide advantageous refinements of the invention.

In the case of an electrical-hydraulic method for increasing the oil yield from petroleum deposits with water- and oil-bearing rock formations,

-   -   a) at least one steel-tube casing assigned to a conventional         production well during pumping operation is used as an electrode         and an electrical feeder and at least one underground metal         structure are used as a counter electrode,     -   b) producing inflow zones of the production well establish an         electrical coupling to at least one water- and oil-bearing rock         formation,     -   c) a water/oil recovery flow comprising a water volume fraction         and an oil volume fraction flows through a recovery pipeline,         which is designed such that it is electrically insulated from         the steel-tube casing,     -   d) an electrode formed by the lower part of the steel-tube         casing of the production well has an electrical contact surface         with respect to an electrolytically conductive water/oil liquid         mixture in the well and, via the inflow zone, an electrical         contact surface with respect to the rock formation,     -   e) an electrical connecting line is formed between the surface         above ground and the electrode comprising the upper part of the         steel-tube casing of the production well, an electrical         insulation of the connecting line being formed inwardly by an         air-filled annular space present between the production well and         the steel-tube casing and outwardly with respect to the rock by         means of an existing high-impedance cement filling in the         annular space between the steel-tube casing and the wall of the         well,     -   f) at least one electrical contact terminal is provided on a         steel-tube drill head of the production well and at least one         electrical contact terminal is provided on the counter         electrode,     -   g) an alternating current source with an assigned power         converter is installed on the surface above ground and there is         an electrical cable connection between the power converter and         the electrical contact terminals, and     -   h) a recovery pump in the recovery line of the production well,         which has an electrical insulation with respect to the recovery         pipeline and, as a result of the chopped volume-portioned pump         operation, accomplishes an electrical insulation of the         hydraulic recovery flow in the pump,     -   i) a pressure-driven hydraulic water/oil volume flow is         continuously produced in the rock formation by the operation of         the pump in the production well,     -   j) during a stimulation phase, an electrical alternating field         is overlaid on the hydraulic flow field,     -   k) the electrical alternating field is generated in a controlled         manner by the power converter, continuous cycles of functionally         variable alternating current in a low-frequency spectrum, in         particular in a frequency spectrum of >0 Hz to 500 Hz, being fed         in via the electrode and the counter electrode and oscillating         electrical currents of the cation and anion charge carriers         being caused thereby in the water- and oil-bearing rock         formation,     -   l) an increase in the surface charge density is caused in the         finely porous, predominantly oil-saturated regions of the rock         formation by the oscillating motion of the cation and anion         charge carriers, which in turn brings about a lowering of the         interfacial viscosity and surface tension and also an increase         in the electrical repulsion between oil droplets and the rock         matrix, whereby the permeability and flow characteristics are         improved,     -   m) a mixing process with an increase in the contact surfaces and         mass transfers between water and oil is produced in the highly         permeable, predominantly water-bearing flow path zones of the         rock formation by the oscillating motion of the cation and anion         charge carriers, forming highly viscous water/oil emulsions,         which cause a blocking of the highly permeable zones,     -   n) the blocking of the highly permeable flow path zones together         with pressure-driven volumetric flow and electrical stimulation         have the effect that additional previously unextractable amounts         of oil are mobilized and at the same time new flow paths for         further transport are created.

The advantages achieved are in particular that, in comparison with conventional tertiary oil extraction methods, no complex and expensive injection bores and additional infrastructure installations are required and no environmentally harmful effects are caused and also there is no depth limitation. In comparison with other electrical tertiary methods, apart from the improved degree of oil extraction, it is also the case that no additional deep bores or wells are necessary and no additional internals are required in production wells. Correspondingly, production downtimes that arise in the time taken for running the drillstring in, through and out can be prevented by the new method. Further advantages are the flexible use for vertical, inclined and horizontal bores of various running-in and out operations and also the quick and inexpensive installation and implementation. Altogether, a considerable economic benefit is obtained, comprising on the one hand an increase in oil yield and saving of water drainage costs as compared with extraction exclusively by pumping (primary and secondary recovery) and on the other hand the much lower cost per unit volume for the oil additionally produced in comparison with other tertiary methods.

With the electrical-hydraulic oil extraction method, there is an increase in the volume of petroleum produced in comparison with conventional pumping as a result of the feeding of low-frequency alternating current into water- and oil-bearing rock formations of petroleum deposits. Existing internals of production wells are thereby used as electrodes and counter electrodes and also as an electrical line, and the electrical stimulation is carried out during the pumping. The electrical excitation at the same time brings about in-situ mixing and mobilizing processes and also the generation of new flow paths, whereby additional amounts of oil can be extracted, in particular from the finely porous regions of rock.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail below on the basis of an exemplary embodiment with reference to the associated drawing, in which:

FIG. 1 shows a schematic representation of a section of the components of the device according to the invention and also the operating principle of the method and

FIG. 2 shows a representation of an oil fraction/time diagram with a representation of the result of using the method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to FIG. 1, the existing steel-tube casing in a production well 1 is used as an electrical connecting line 11 and electrode 10 and a remote metal structure 2 is used as a counter electrode, in order to feed low-frequency electrical alternating current into the water- and oil-bearing rock formation 4 of a petroleum deposit by means of a salty electrolytically conductive water/oil liquid mixture 9 b in the well and the inflow zones 3, whereby an oscillating motion of the cation and anion charge carriers 20 contained in the salty water is brought about there. In this case, the functionally and frequency-variable alternating current is generated from a three-phase power supply 16 by a power converter 15, which is set up on the surface above ground 12 and is connected via electrical cable connections 17 to electrical contact terminals 14 on the drill head of the production well 1 and the head of the metal-stake counter electrode. For the method to be functionally operational, an electrical insulation of the following three component parts is required: the steel-tube connecting line 11, a recovery pipeline 5 and a recovery flow 9 a. This is achieved by the following existing components: a high-impedance annular-space cement filling 13 between the steel-tube connecting line 11 and the wall of the well with respect to the rock, an air-filled annular space 8 between the recovery pipeline 5 and the steel-tube connecting line 11, a plastic or rubber annular packer 6, an outer-tube insulation 7 between the recovery pipeline 5 and the steel-tube drill head and an insulated recovery pump 18. The latter acts as an insulating interruption of the electronic conductivity of the metallic recovery pipeline 5, on the one hand because of individual plastic components and on the other hand because of the operation of the pump itself, the electrolytic conductivity of the liquid recovery flow 9 a being interrupted by the chopping into air-separated volumetric portions, so that the hydraulic recovery flow 9 a above the recovery pump 18 can no longer carry an electrical current. As a result of the simultaneous operation of the recovery pump 18 and the power converter 15, in the producing rock formation 4 a hydraulic flow field is overlaid with an electrical alternating field, and correspondingly the water/oil volumetric flow 19 is overlaid with an oscillating flow comprising cation and anion charge carriers 20. In the highly permeable, predominantly water-carrying flow path zones of the rock formation, this leads to thorough mixing of water and oil, and consequently to the formation of highly viscous water-oil emulsions, which cause a blocking of the highly permeable zones. At the same time, a mobilization of oil droplets is brought about in the finely porous, predominantly oil-saturated regions of the rock formation by the electrical stimulation. The overall result of the interaction of the two effects is that previously unextractable amounts of oil are mobilized and at the same time new flow paths for further transport are created.

FIG. 2 shows the variation over time of the measured oil volume fraction of the water/oil recovery flow 9 a that is extracted from a production well 1 when the pump is operating, to be specific before, during and after a stimulation phase 21, during which the electrical excitation according to the method was applied. Up until the beginning of the stimulation phase, the oil fraction data curve 22 has a downward trend, as typically encountered as a result of the increasing incursion of water in the case of primary and secondary oil extraction measures. The trend can be statistically represented by a dashed regression line 24, which indicates at the zero percent line the theoretically temporal end of the extraction of oil when exclusively using a pump, from which the maximum oil recovery volume (petroleum yield) from the moderately and highly permeable regions of the rock formation 4 can be calculated. By the electrical stimulation, the oil fraction of the overall water/oil delivery flow is increased with respect to the regression line 24 or with respect to the zero percent line during and after the stimulation phase 21. The additional volume of oil extracted per unit of time that is substantially recovered from the finely porous and low-permeable regions of the rock formation is obtained from the corresponding differential oil fraction 23 after multiplication by the constant overall water/oil production rate.

LIST OF REFERENCE NUMERALS

-   1 Production well -   2 Metal structure -   3 Inflow zone -   4 Rock formation -   5 Recovery pipeline -   6 Annular packer -   7 Outer-tube insulation -   8 Annular space -   9 a Recovery flow -   9 b Liquid mixture -   10 Electrode -   11 Connecting line -   12 Surface above ground -   13 Cement filling -   14 Contact terminal -   15 Power converter -   16 Three-phase power supply -   17 Electrical cable connection -   18 Recovery pump -   19 water/oil volume flow -   20 Charge carrier -   21 Stimulation phase -   22 Oil fraction data curve -   23 Differential oil fraction -   24 Regression line 

1. An electrical-hydraulic method for increasing the oil yield from petroleum deposits with water- and oil-bearing rock formations in which a) at least one steel-tube casing assigned to a conventional production well (1) during pumping operation is used as an electrode and an electrical feeder and at least one underground metal structure (2) are used as a counter electrode, b) producing inflow zones (3) of the production well (1) establish an electrical coupling to at least one water- and oil-bearing rock formation (4), c) a water/oil recovery flow (9 a) comprising a water volume fraction and an oil volume fraction flows through a recovery pipeline (5), which is designed such that it is electrically insulated from the steel-tube casing, d) an electrode (10) formed by the lower part of the steel-tube casing of the production well (1) has an electrical contact surface with respect to an electrolytically conductive water/oil liquid mixture (9 b) in the well and, via the inflow zone (3), an electrical contact surface with respect to the rock formation, e) an electrical connecting line (11) is formed between the surface above ground (12) and the electrode (10) comprising the upper part of the steel-tube casing of the production well (1), an electrical insulation of the connecting line (11) being formed inwardly by an air-filled annular space (8) present between the production well (1) and the steel-tube casing and outwardly with respect to the rock by means of an existing high-impedance cement filling (13) in the annular space between the steel-tube casing and the wall of the well, f) at least one electrical contact terminal (14) is provided on a steel-tube drill head of the production well (1) and at least one electrical contact terminal is provided on the counter electrode, g) an alternating current source with an assigned power converter (15) is installed on the surface above ground and there is an electrical cable connection (17) between the power converter (15) and the electrical contact terminals (14), and h) a recovery pump (18) in the recovery line of the production well (1), which has an electrical insulation with respect to the recovery pipeline (5) and, as a result of the chopped volume-portioned pump operation, accomplishes an electrical insulation of the hydraulic recovery flow in the pump, characterized in that i) a pressure-driven hydraulic water/oil volume flow (19) is continuously produced in the rock formation (4) by the operation of the pump in the production well (1), j) during a stimulation phase (21), an electrical alternating field is overlaid on the hydraulic flow field, k) the electrical alternating field is generated in a controlled manner by the power converter (15), continuous cycles of functionally variable alternating current in a low-frequency spectrum being fed in via the electrode (10) and the counter electrode and oscillating electrical currents of the cation and anion charge carriers (20) being caused thereby in the water- and oil-bearing rock formation (4), l) an increase in the surface charge density is caused in the finely porous, predominantly oil-saturated regions of the rock formation (4) by the oscillating motion of the cation and anion charge carriers (20), which in turn brings about a lowering of the interfacial viscosity and surface tension and also an increase in the electrical repulsion between oil droplets and the rock matrix, whereby the permeability and flow characteristics are improved, m) a mixing process with an increase in the contact surfaces and mass transfers between water and oil is produced in the highly permeable, predominantly water-bearing flow path zones of the rock formation (4) by the oscillating motion of the cation and anion charge carriers (20), forming highly viscous water/oil emulsions, which cause a blocking of the highly permeable zones, n) the blocking of the highly permeable flow path zones together with pressure-driven volumetric flow and electrical stimulation have the effect that additional previously unextractable amounts of oil are mobilized and at the same time new flow paths for further transport are created.
 2. The method as claimed in claim 1, characterized in that, by the operation of the pump in the production well (1), the in-situ mobilized additional amounts of oil are extracted from the rock formation (4) during and after the electrical stimulation phase (21), whereby the percentage oil volume fraction (22) in the water/oil volume flow (19) in the differential comparison (23) is increased with respect to the oil fraction regression curve (24) or with respect to the zero percent line, the oil fraction regression curve being determined by means of regression analysis on the basis of data from extraction exclusively by pumping in the time period before the electrical stimulation.
 3. The method as claimed in claim 1, characterized in that the additional volume of oil extracted per unit of time is determined by means of the differential oil fraction (23) multiplied by the constant overall water/oil production rate and the overall oil recovery volume and the degree of oil extraction are increased in comparison with extraction exclusively by pumping by the activation of the additional oil volume from the finely porous regions of the rock formation (4).
 4. The method as claimed in claim 1, characterized in that the alternating current in a frequency spectrum of >0 Hz to 500 Hz is fed in via the electrode (10) and the counter electrode.
 5. A device for carrying out the method as claimed in claim 1 comprising: a) at least one steel-tube casing assigned to a conventional production well (1) during pumping operation, which is formed as an electrode (10) and an electrical feeder, and at least one underground metal structure (2) serving as a counter electrode, the production well (1) having producing inflow zones (3) for the electrical coupling to at least one water- and oil-carrying rock formation (4), a recovery pipeline (5) of the production well (1) being designed such that it is electrically insulated from the steel-tube casing, b) at least one electrode (10), which is formed by the lower part of the steel-tube casing of the production well (1), which has an electrical contact surface with respect to the electrolytically conductive water/oil liquid mixture (9 b) in the well and, via the inflow zone (3), an electrical contact surface with respect to the rock formation (4), c) at least one electrical connecting line (11) between the surface above ground and the electrode (10), which is formed by the upper part of the steel-tube casing of the production well (1) and is designed such that it is electrically insulated, d) at least one electrical contact terminal (14) on a steel-tube drill head of the production well (1) and at least one electrical contact terminal on the counter electrode, e) an alternating current source installed on the surface above ground with an assigned power converter (15) and an electrical cable connection (17) between the power converter (15) and the electrical contact terminals (14), and f) a recovery pump (18) in the recovery line of the production well (1), which has an electrical insulation with respect to the recovery pipeline (5) and, as a result of the chopped volume-portioned pump operation, accomplishes an electrical insulation of the hydraulic recovery flow in the pump.
 6. The device as claimed in claim 5, characterized in that the counter electrode is part of the steel-tube casing of a further production well.
 7. The device as claimed in claim 5, characterized in that the production well (1) is electrically insulated with respect to the steel-tube casing by means of an annular packer seal (6), an outer-tube insulation (7) and the air-filled annular space (8).
 8. The device as claimed in claim 5, characterized in that the water/oil liquid mixture (9 b) is in the section of the well below the annular packer seal (6).
 9. The device as claimed in claim 5, characterized in that the power converter (15) is connected to an electrical power supply (16) formed as a three-phase alternating current supply. 